Air cycle food freezing system and method

ABSTRACT

A refrigeration system for freezing of food products, utilizing air as the working fluid. The system includes a freezing chamber having entrance and exit ports for passing a food product therethrough. A refrigerant supply main provides low temperature air to the freezer chamber, which air exits from the chamber via a return main. The warmed air passes through first and second stage compressors and aftercoolers positioned in line beyond each said compression stage. The high pressure output from the second stage compressor and aftercooler is also passed in countercurrent relationship through a heat exchanger, the cooler side of which carries the low pressure return flow of air refrigerant on its way to the first stage compressor. The compressed and cooled air from the compressor stages passes through an expansion turbine where the work performed thereby cools the air to the desired low temperature, and the cold air is then lead into the supply main leading back to the freezer chamber. A make-up and drier system, including a pair of drying beds, is connected to provide dry make-up air to the refrigerant return main to replace air lost at the product entrance and exit ports of the freezer chamber. The beds are so arranged that regeneration of one of the pair may be effected while the other is on line.

[limited States Patent 1 Linhardt et al.

in] 3,868,827 1 Mar. 4, 1975 AIR CYCLE FOOD FREEZING SYSTEM AND METHOD [75] Inventors: Hans D. Linhardt, Costa Mesa;

Thomas A. Carter, Whittier; James A. Kirk, Costa Mesa, all of Calif.

[73] Assignee: Airco, Inc., Montvale, NJ.

[22] Filed: Apr. 5, 1973 [21] Appl. No.: 348,410

FOREIGN PATENTS OR APPLICATIONS 2,064 7/1857 Great Britain 13.466 11/1885 Great Britain Primary E.\'aminerMeyer Perlin Assistant E.\'aminerRonald C. Caposella Attorney, Agent, or FirmRoger M. Rathbun;

Edmund W. Bopp; H. Hume Mathews [57] ABSTRACT A refrigeration system for freezing of food products. utilizing air as the working fluid. The system includes a freezing chamber having entrance and exit ports for passing a food product therethrough. A refrigerant supply main provides low temperature air to the freezer chamber, which air exits from the chamber via a return main. The warmed air passes through first and second stage compressors and aftercoolers positioned in line beyond each said compression stage. The high pressure output from the second stage compressor and aftercooler is also passed in countercurrent relationship through a heat exchanger, the cooler side of which carries the low pressure return flow of air refrigerant on its way to the first stage compressor. The compressed and cooled air from the compressor stages passes through an expansion turbine where the work performed thereby cools the air to the desired low temperature, and the cold air is then lead into the supply main leading back to the freezer chamber. A make-up and drier system, including a pair of drying beds, is connected to provide dry make-up air to the refrigerant return main to replace air lost at the product entrance and exit ports of the freezer chamber. The beds are so arranged that regeneration of one of the pair may be effected while the other is on line.

10 Claims, 1 Drawing Figure FREEZER BOX PATENIED MAR 4|97S FREEZER BOX AIR CYCLE FOOD FREEZING SYSTEM AND METHOD BACKGROUND OF INVENTION This invention relates generally to refrigeration systems, and more specifically relates to a food freezing system, utilizing air as the working fluid therein.

Air has long been recognized as a beneficial and economical source of refrigeration in food processing preparations. Air, when thermodynamically reduced to temperatures including cryogenic temperatures, permits very rapid freezing or chilling of many food products, and thus enables a better product with respect to quality and weight retention.

The concept of utilizing air as a working fluid in a refrigeration cycle has been known for many years. In particular, as early as the 19th century, the engineer, George Brayton, proposed a refrigeration machine operating on a cycle since known as the Brayton cycle. The working fluid in the proposed machine received heat at a specified low pressure and temperature, which heat was subsequently extracted at a specified higher pressure and temperature. Although over the intervening years numerous proposals have been forthcoming for utilizing the Brayton cycle in refrigeration apparatus, by and large the cycle has not come into widespread use for such purposes. Of at least equal pertinenee for present purposes, is the fact that such a cycle has not, in spite of much past research and effort, been applied on a commercial scale to freezing operations, wherein very low temperatures are required for efficient operation.

In accordance with the foregoing, it may be regarded as an object of the present invention, to provide a food freezing system utilizing air as the working fluid in the refrigerant cycle thereof.

It is a further object of the present invention, to provide a food freezing system utilizing air as the working fluid in a refrigeration cycle which is semi-closed, and wherein provision is present in the system for replacing air lost during cycle operation, by dried make-up air admitted in regulated quantities into the said cycle.

It is a further object of the present invention, to provide a food freezing refrigeration system utilizing air as the working fluid, which is of simple, dependable and compact construction, and which is adapted for dependable continuous operation thereof.

SUMMARY OF INVENTION Now in accordance with the present invention, the foregoing objects, and others as will become apparent in the course of the ensuing specification, are'achieved in a food-freezing system utilizing a refrigeration cycle wherein air is the working fluid. The system includes a freezing chamber having entrance and exit ports for passing a food product therethrough. Cold air at a temperature of the order of 200F flows from the refrigerant supply main into the freezing chamber. A temperature control system at the said chamber maintains the proper cold air flow and pressure balance at the chamber supply and return mains to maintain chamber temperature consistent with product freezing demands. The warmer exit air from the freezer chamber (typically at about 80F) passes into the return main, thence through the low pressure pass of a regenerative heat exchanger, and then into the suction portion of a first stage compressor. The compressed air from the first stage compressor is passed through an intercooler, thence through a second stage compressor, and an aftercooler. The compressed and cooled air then proceeds through the high pressure pass of the aforementioned regenerative heat exchanger, where the temperature is reduced by exchanging heat with the countercurrent low pressure return air stream. Upon exiting this exchanger, the cooled air enters an expansion turbine (which drives the second stage compressor) where its energy is transferred to the compressor with a resulting drop in air temperature. The air, now at a temperature of about -200F flows into the refrigerant supply main, for furnishing to the freezer chamber.

The freezer chamber is preferably maintained at a slightly positive pressure, and a certain amount of air leakage occurs at the normally open entrance and exit ports for the food product. A make-up and drier system replaces leaked air by feeding dried air obtained from atmosphere into the return main. The make-up and drier system preferably includes at least a pair of drier beds, one of which may be placed on line, while the alternate bed is being regenerated. For the latter purposes a stream of warm air may be bled from first stage compressor and passed through a heater before being fed to the drier bed undergoing regeneration. Alternately, make-up air may be cooled to a desired cryogenic temperature, e.g., 200F, whereupon the cooled airis passedto an ice'separator prior to the introduction of such cooled air into the freezer chamber.

BRIEF DESCRIPTION OF DRAWING The invention is diagrammatically illustrated by way of example in the drawing appended hereto, in which:

The FIGURE is a schematic flow diagram, setting forth the basic elements of an air cycle food freezing system in accordance with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT In the FIGURE an air cycle food freezing system 10 is set forth including generally a freezer chamber 12, and a refrigeration unit 14. The latter supplies cold, refrigerant air to freezer chamber 12 via supply main 16, and receives a return flow of warmer air from the chamber via return main 18. The freezer chamber 12 is not per se of the present invention, but may typically comprise an enclosed box having a normally open input port 20, and normally open output port 22, for passing food products through the chamber on a moving conveyor belt, preferably wound in a continuous helix between the input and output ports. Freezing chamber 12 while differing with respect to the manner in which the refrigerant is fed therein and through, otherwise has a product feed and travel arrangement similar to that described in pending US. Pat. application No. 170,175 now US. Pat. No. 3,733,848, assigned to Airco, Inc., the assignee of the instant application.

It will be appreciated in considering the FIGURE that supply main l6 and return main 18, may typically extend beyond the left-hand side of the FIGURE, and that additional freezer chambers beyond the single chamber 12 shown may be serviced by a refrigeration unit, such as that at 14. Furthermore, additional refrigeration units, such as at 14, may be arranged in parallel to connect to the supply and return mains in the same manner as is the single refrigeration unit shown. Indeed a typical plant installation utilizing the configuration shown in the FIGURE, may have of the order of three or more such refrigeration units 14, and typically of the order of sixteen or more freezer chambers.

Flow into freezer chamber 12 from supply main 16 passes through conduit 24, the flow through said conduit being controlled by temperature indicating controller 26, which acts through control valve 28. Flow of relatively warmer air from the freezer chamber proceeds outwardly by conduit 30, which is controlled through valve 32 by means of pressure indicating controller 34. The flow between the two mains is also regulated through the adjusting valve 36 in bypass loop 38 between the mains. Whereas the cold air entering the freezer chamber is typically provided from supply main 16 at a temperature of the order of 200F, the return main typically has air therein at a temperature of about .-80F.

Air from return main 18 is fed to refrigerant unit 14 via conduit 40. The latter is regulated by a control valve 42, in turn operated by temperature indicating controller 44 which balances the flow in accordance with flow conditions in conduit 46 leading back from refrigeration unit 14 to supply main 16. The air from conduit 40 thence passes through the low pressure pass 48 of a regenerative heat exchange 50. A by-pass line 41 and valve 43, located just before heat exchanger 50, provides for cool-down. The air stream then proceeds via conduit 52 to the input of first stage compressor 54. After being compressed in the latter, the heated and compressed air from the compressor outlet proceeds via conduit 53 and an expansion portion 57, through an intercooler 58. The latter is water-cooled by water supply proceeding from water line 60 through connecting conduit 62, said water supply exiting via conduit 64 and valve 66 back into the return water conduit 68. The water cooling input main appears at 70 and the water return main at 72, with valves for conduits 60 and 68 appearing at 71 and 73. These latter elements may, of course, supply various additional refrigerating units such as 14, as previously mentioned.

The cooled air then proceeds from intercooler 58 by conduit 74 to the input of second stage compressor 76, where the air stream is further compressed, and in consequence, heated. A surge line 77 and surge control valve 79 are provided across conduits 74 and 52 to enable control of surging from compressor 76. Upon emerging from the output of second stage compressor 76, the thus further heated air is passed through an aftercooler 78, which again iswater-cooled from the lines 60 and 68, referred to in connection with intercooler 58. The water input in the present case is regulated by a valve80. The now cooled air emerging from aftercooler 78 passes through the high pressure pass 82 of regenerative heat exchanger 50, previously referred to, where the air stream is further cooled by countercurrent exchange with the relatively cold air in low pressure pass 48. The air stream nowproceeds through conduit 84 to the input of expansion turbine 86. The latter is mechanically coupled to compressor 76, and may be commonly journaled for rotation therewith at a bearing system 88. The latter is seen to be provided with lubrication via the oil lines 89 and 90, which lines are connected to the lubrication oil system 92, of conventional construction including pumping means and so forth. The same lubrication oil system 92 is also seen to provide lubrication via the pair of lines 94 and 96 to the gear box 98 which drives first stage compressor 54. The gear box 98, in turn, is driven by a suitable motor 100. A pair of water lines 102 and 104 are connected from lines 60 and 68, to in turn provide water cooling to lubrication oil system 92. The control valve 106 regulates the water flow to system 92 in accordance with the temperature detected by sensor 108 at the lubricant line 89 which carries the outflow from the oil system.

Air thus emerging from the outlet of expansion turbine 86 passes through conduit 110 and regulatory valve 112, and thence proceeds via conduit 46 into the supply main 16. The air at this point is at a temperature of the order of 200F and, as discussed previously. is then fed directly into the freezer chamber 12.

As has been mentioned previously herein, the freezing chamber 12 is provided with entrance port 20 and exit port 22 for allowing passage of the product to be treated therein. These ports are normally open to ambient atmosphere. In order to avoid leakage of moist ambient air within the chamber, the said chamber is preferably operated at a slightly positive pressure with respect to atmosphere. In consequence, a degree of leakage normally occurs from the chamber to atmosphere. In order to provide a make-up source of clean, dry air to replace that lost by such leakage (as well as losses due to other possible leakage sources) a make-up and drier system 114 is provided. In accordance with pressure and flow conditions detected in line 116 con nected to return main 18, the control means 120 linked by control line 122 and pressure transmitter 121 to the monitored point on line 18, varies the position of regulatory valve 122 to permit influx of make-up atmospheric air via line 124. The admitted air passes through conduit 126, and thence through valve 131 or 132 to one of the pair of drier beds 128 or 130, depending upon which bed is presently on line. The 128, 130 beds are conventional elements which act to dry the admitted air and may, for example, comprise so-called molecular sieves. The flow of air, assuming for purposes of analysis to be through bed 130, thus passes through valves 132 and 136, thence through conduit 138 and 140, and thus into the return main 18 to provide the desired make-up flow.

During the continued use of one or the other of the beds 128 and 130, it becomes necessary to remove the moisture therefrom in order to regenerate the bed. In order to effectively accomplish this purpose, heated air is withdrawn from the outlet of first stage compressor 54 via the line 142 and valve 144. This heated air thence is seen to proceed to the line 146 and passed through a heater 148. Depending then upon the positions of the respective valves or 152 (in parallel lines leading from drier 148), the further heated air may pass to one or the other of the beds 128 or 130. Assuming, as previously indicated, that bed 130 is on line, valve 150 is closed and 152 opened, so that heated air may proceed through the line 154 and bed 128 to regenerate said bed. The air upon exiting from the bed 128 passes through valve 156, and thence proceeds via line 158 back to atmosphere. Periodically, of course, the regenerated bed, in this case bed 128, is placed on line and the alternate bed 130 regenerated by appropriately changing the position of the valves. That is to say, in order to now regenerate bed 130, valve 150 is opened, as is valve 160, so that the heated air may flow through the valve 150, thence through conduit 162 and 164, through bed 130, then through valve 160 and conduit 158 to atmosphere.

While the present invention has been particularly set forth in terms of specific embodiments thereof, it will be evident to those skilled in the art, that numerous variations upon the invention are now enabled, which variations yet reside within the scope of the instant teaching. Accordingly, the invention is to be broadly construed, and limited only by the scope and spirit of the claims now appended hereto.

We claim:

1. A food freezing system utilizing air as the working refrigeration fluid, comprising in combination:

a freezing chamber, having entrance and exit ports and means for passing a food product through said freezing chamber;

a refrigerant supply main connected to said freezer chamber for supplying refrigerant air to effect freezing operations;

a return main for receiving warmed air from said chamber;

first stage compressor means connected for receiving the output from said return main and compressing said air to a predetermined pressure;

intercooling means connected in the air stream flow line proceeding from said first stage compressor means, for cooling said compressed air;

second stage compressor means connected to receive the output from said intercooling means, and adapted to further compress said air;

aftercooling means positioned to receive the further compressed air output from said second stage compressor means, and cool said further compressed air;

regenerative heat exchanger means connected to re ceive the compressed air from said aftercooler means and further cool said air by heat exchange with at least a portion of the warmed air in said return main from said freezer chamber; and

expansion turbine means for receiving the further cooled air from said regenerative heat exchanger and cooling said air to cryogenic temperatures by extracting heat energy therefrom, said turbine means being connected to supply said expanded cooled air to said supply main.

2. Apparatus in accordance with claim 1, wherein said expansion means is mechanically coupled to said second stage compressor means.

3. Apparatus in accordance with claim 2, wherein said intercooler means and said aftercooler means are each water cooled.

4. Apparatus in accordance with claim 1, wherein said entrance and exit ports of said freezing chamber are at least partially open to atmosphere, whereby air leaks between said system and ambient atmosphere; and further including make-up air drier means connected between atmosphere and said return main for providing dry make-up air to said system to replace said leaked air.

5. Apparatus in accordance with claim 4, wherein said freezer chamber is maintained at a slightly positive pressure with respect to atmosphere, to minimize leakage of moist air inwardly to said chamber from atmosphere.

6. Apparatus in accordance with claim 5, wherein said make-up and drier means includes: at least a pair of regeneratable drier beds; heater means for regenerating said beds; and means for selectively connecting one of said beds to said heater means to regenerate said beds and place said other bed on line to said return main.

7. Apparatus in accordance with claim 6, wherein said drier beds comprise molecular sieves.

8. A method of refrigerating articles comprising the steps of:

a. supplying cold refrigerant air at a first predetermined temperature to a substantially enclosed chamber, to directly contact said articles therein;

b. continuously withdrawing a portion of the refrigerant air from said chamber at a second predetermined temperature above the first predetermined temperature after contacting said articles with refrigerant air;

c. compressing the withdrawn refrigerant air to a first pressure;

d. cooling the compressed refrigerant air and further compressing the cooled refrigerant air to a second pressure;

6. further cooling the further compressed refrigerant air to a temperature above the first predetermined temperature by heat exchange with at least a portion of the withdrawn refrigerant air from said chamber at the second predetermined temperature; and

. expanding the further cooled refrigerant air to extract heat energy therefrom to cool the refrigerant air to said first predetermined temperature for sup plying the refrigerant air to said substantially enclosed chamber.

9. A method of refrigerating articles as defined in claim 8 further including the step of:

introducing make-up air to the refrigerant air stream at or downstream of the chamber.

it). A semi-closed refrigeration system utilizing air as the working refrigeration fluid, comprising in combination:

a chamber for containing products to be refrigerated;

a refrigerant supply main connected to said chamber for supplying cold air to effect refrigeration of the products;

a return main for receiving warmed air from said chamber;

first compressor means connected to receive the warmed air from said return main, and compressing said air to a predetermined. pressure;

intercooling means for cooling said compressed air from said first compressor means;

second compressor means connected to receive the air from said intercooling means, and adapted to further compress said air;

aftercooling means positioned to receive the further compressed air output from said second compressor means, and cool said further compressed air;

regenerative heat exchanger means adapted to further cool output air from said aiftercooler means by heat exchange with the warmed air from said chamber, for precooling said output air prior to ex pansion thereof; and

means to isentropically expand the cooled air from said regenerative heat exchanger to cool said air to cryogenic temperatures by extracting heat energy therefrom, said expansion means being connected to supply said cooled air to said supply main.

l l= =l= 

1. A food freezing system utilizing air as the working refrigeration fluid, comprising in combination: a freezing chamber, having entrance and exit ports and means for passing a food product through said freezing chamber; a refrigerant supply main connected to said freezer chamber for supplying refrigerant air to effect freezing operations; a return main for receiving warmed air from said chamber; first stage compressor means connected for receiving the output from said return main and compressing said air to a predetermined pressure; intercooling means connected in the air stream flow line proceeding from said first stage compressor means, for cooling said compressed air; second stage compressor means connected to receive the output from said intercooling means, and adapted to further compress said air; aftercooling means positioned to receive the further compressed air output from said second stage compressor means, and cool said further compressed air; regenerative heat exchanger means connected to receive the compressed air from said aftercooler means and further cool said air by heat exchange with at least a portion of the warmed air in said return main from said freezer chamber; and expansion turbine means for receiving the further cooled air from said regenerative heat exchanger and cooling said air to cryogenic temperatures by extracting heat energy therefrom, said turbine means being connected to supply said expanded cooled air to said supply main.
 2. Apparatus in accordance with claim 1, wherein said expansion means is mechanically coupled to said second stage compressor means.
 3. Apparatus in accordance with claim 2, wherein said intercooler means and said aftercooler means are each water cooled.
 4. Apparatus in accordance with claim 1, wherein said entrance and exit ports of said freezing chamber are at least partially open to atmosphere, whereby air leaks between said system and ambient atmosphere; and further including make-up air drier means connected between atmosphere and said return main for providing dry make-up air to said system to replace said leaked air.
 5. Apparatus in accordance with claim 4, wherein said freezer chamber is maintained at a slightly positive pressure with respect to atmosphere, to minimize leakage of moist air inwardly to said chamber from atmosphere.
 6. Apparatus in accordance with claim 5, wherein said make-up and drier means includes: at least a pair of regeneratable drier beds; heater means for regenerating said beds; and means for selectively connecting one of said beds to said heater means to regenerate said beds and place said other bed on line to said return main.
 7. Apparatus in accordance with claim 6, wherein said drier beds comprise molecular sieves.
 8. A method of refrigerating articles comprising the steps of: a. supplying cold refrigerant air at a first predetermined temperature to a substantially enclosed chamber, to directly contact said articles therein; b. continuously withdrawing a portion of the refrigerant air from said chamber at a second predetermined temperature above the first predetermined temperature after contacting said articles with refrigerant air; c. compressing the withdrawn refrigerant air to a first pressure; d. cooling the compressed refrigerant air and further compressing the cooled refrigerant air to a second pressure; e. further cooling the further compressed refrigerant air to a temperature above the first predetermined temperature by heat exchange with at least a portion of the withdrawn refrigerant air from said chamber at the second predetermined temperature; and f. expanding the further coolEd refrigerant air to extract heat energy therefrom to cool the refrigerant air to said first predetermined temperature for supplying the refrigerant air to said substantially enclosed chamber.
 9. A method of refrigerating articles as defined in claim 8 further including the step of: introducing make-up air to the refrigerant air stream at or downstream of the chamber.
 10. A semi-closed refrigeration system utilizing air as the working refrigeration fluid, comprising in combination: a chamber for containing products to be refrigerated; a refrigerant supply main connected to said chamber for supplying cold air to effect refrigeration of the products; a return main for receiving warmed air from said chamber; first compressor means connected to receive the warmed air from said return main, and compressing said air to a predetermined pressure; intercooling means for cooling said compressed air from said first compressor means; second compressor means connected to receive the air from said intercooling means, and adapted to further compress said air; aftercooling means positioned to receive the further compressed air output from said second compressor means, and cool said further compressed air; regenerative heat exchanger means adapted to further cool output air from said aftercooler means by heat exchange with the warmed air from said chamber, for precooling said output air prior to expansion thereof; and means to isentropically expand the cooled air from said regenerative heat exchanger to cool said air to cryogenic temperatures by extracting heat energy therefrom, said expansion means being connected to supply said cooled air to said supply main. 